Watt-hour meters, most commonly used as electric energy billing meters, are simple induction electromechanical meters. These meters have proven to have a high degree of accuracy and reliability through many years of service under varying ambient operating conditions. The reliability of these meters is exemplified by the fact that accrediting authorities in countries such as Canada require only sample testing of meters after which the meters can be sealed for a period of twelve years. This seal can be indefinitely extended for periods of up to eight years, depending upon the accuracy criteria of the testing.
The watt-hour meter includes a motor, a magnetic brake and a register. The torque of the motor is proportional to the power flowing through it. The magnetic brake is used to retard the speed of the motor in such a way that the rotation speed is proportional to the power flowing through it (by making the braking effect proportional to the speed of the rotor). The register is used to count the number of revolutions the motor makes. The rotor portion of the meter motor is an electrical conductor in the form of a disc which is placed between the pole faces of the stator. Magnetic fluxes induce emf's in the disc which cause eddy currents that react with the alternating magnetic field, causing torque on the disc. Since the disc is free to turn, the torque causes it to rotate. Since the torque tends to cause constant acceleration, brake magnets are placed around the disc. The strength of the magnet is chosen so that the retarding torque will balance the driving torque at a given speed.
More complex forms of such meters are electronic meters using solid-state electronic circuits. These meters have the advantage of providing greater varieties of modes of measuring operations, including measurements of different parameters of electric energy consumption such as, for example, periods of "peak" and "off peak" periods of usage. Electronic meters also provide the advantage of remote reading, for example, by land lines (either power transmission lines or telephone lines).
A meter of intermediate complexity is an electromechanical meter with electronic components associated therewith and which normally are mounted inside the meter housing.
The latter two meters are not as reliable as simple electro-mechanical meters. This is exemplified by the fact that accrediting authorities in Canada require each meter to be tested and then only allow them to remain in the field for a maximum period of six years, after which time they must each be removed and reverified before being returned to the field for further use. This creates a much higher operating cost for the electric utility companies.
Solid-state electronic circuit billing meters, electro-mechanical induction billing meters and the latter form of meters incorporating electronic circuits are all required to perform in the same ambient environments and all physically have a transparent cup-shaped cover attached to a base which together form an enclosure for the operating mechanism. In all three instances the base is the same and attaches to existing meter sockets of common construction.
There is a growing demand for electricity, and existing electric utilities forecast a supply shortage by the year 2000. This shortage leaves them three options: either (a) create new generating facilities, (b) purchase power from independent producers, or (c) conserve energy. One or more of these three alternatives may be implemented by electrical utilities. Instead of adding new generating facilities to meet the growing demand for electricity, most utility companies consider it more economical to provide incentives for their customers to modify their electricity usage habits. This approach, by conserving electricity, postpones the need for new generating facilities.
Electric utilities use a process called "Demand Side Management" (DSM) to influence their customers' use of electricity in ways that produce the desired changes in the utilities' electric loads. Electric utilities view DSM as an alternative to the creation of additional generating capacity, however, DSM requires a good understanding of how and why customers use electricity. Electric Utilities are therefore undertaking to gather this information and are using creative rate structures in order to motivate customers to reduce their electric energy consumption. Since the electricity meter is typically a utility's only means of measuring a customer's electric energy usage, varying rate structures are only effective if a meter is capable of correlating the data and making this data available readily and in a useable form. This means that the utilities require more than plain residential watt-hour meters for multi-rate, prepayment, time-of-use and various other functions and measurements.
Enhancing the function of a residential meter traditionally required the addition of application-specific electronics to the meter. This resulted in a sophisticated, highly specialized, and thus expensive meter. Furthermore, the expensive meter would replace and displace a perfectly operational plain meter. It is also noteworthy that such meter replacement involves ongoing updating of detailed meter tracking records.
For the purpose of surveys and/or continued use of additional functions it is not necessarily economic or cost effective to replace traditional reliable electro-mechanical meter with solid state meters.
Examples of multi-function watt-hour meters may be found in U.S. Pat. Nos. 4,881,070, 4,465,970 and 5,014,213.
U.S. Pat. No. 4,465,970 discloses a programmable time-of-use metering system that includes a micro-processing unit incorporating a micro-processor with data input being pulses from a watt-hour meter.
U.S. Pat. No. 5,014,213 discloses a meter that records time-of-use utilizing an electronics module, a power module and a sensor assembly, all of which are located within the meter enclosure provided by the transparent cup-shaped cover that is secured to a base. They disclose optical communication with the electronics module through an optical port, in the transparent cover, to retrieve information by a meter reader from the micromemory.
U.S. Pat. No. 4,881,070 discloses a mechanism within the meter for reading the dials producing output signals for transmitting such readings and other information to a remote location. Related to this is the disclosure of U.S. Pat. No. 4,803,484.
Remote meter reading and transmission of other information from electric meters over the electric power distribution network to a central site is disclosed in U.S. Pat. No. 4,904,995. The patentee discloses a remote transponder unit located within the enclosure of the meter for obtaining information represented by the data from the measuring means of the meter and connection of that transponder unit to the electric distribution system by way of the meter.
U.S. Pat. No. 4,491,789 discloses enhancing the functions of an energy metering meter by incorporating, within the meter enclosure, components which connect to a pulse initiator that responds to rotation of the disc of the meter. The patentee indicates that either a mechanical or electro-mechanical pulse initiator may be used with the rotating disc or alternatively a solid state pulse initiator may be used eliminating the need for a disc.
In the foregoing patented apparatus enhancement of the meter function is accomplished by incorporating additional mechanisms within the meter. This has the disadvantage of shorter approval periods by the accredited authorizing authorities. They do, however, indicate a desire for retro-fitting or maintaining the integrity of the simple electro-mechanical portion of the meter.
U. S. Pat. No. 3,268,884 discloses apparatus for transmitting data from a meter to a remote location by way of telephone lines and utilizes a shaft angle encoder assembly.
As discussed herein before there are disadvantages to enhancing watt-hour meters by incorporating electronic circuits within the meter.
It is thus most desirable to separate the electronics from the conventional electro-mechanical portion of the watt-hour meter but at the same time have a signal generated with a predetermined relationship to the rate of electrical power usage.
Enhancing the function of an electro-mechanical watt-hour meter without incorporating additional apparatus within the meter is known as exemplified by U.S. Pat. Nos. 4,415,853, 4,922,187 and 4,646,003. U.S. Pat. No. 4,646,003 discloses apparatus for verifying the accuracy of a meter and includes, externally of the meter, means for generating a pulse signal responsive to rotation of the disc. A light generating source external to the meter and a light receiving means external to the meter are arranged so that the light beam from the source to the receiver is chopped by the revolving disc which has an aperture near the periphery of the disc that comes into and out of alignment with the beam as the disc rotates. The viewing of the disc is done through the glass cover of the meter. The light generating source and receiver is mounted on arms extending from a casing positionable as an intermediate housing between the meter and the meter receiving socket.
U.S. Pat. No. 4,922,187 discloses a pulse initiator circuit for utility meters where the pulse initiator is attachable to the meter without breaking the meter seal. The pulse initiator circuit detects sensor holes in the watt-hour meter rotor. A source of radiation positioned outside of the watt-hour meter directs a beam toward a receiver and the beam impinges upon the rotor except when aligned with a hole in the rotor. This causes a pulse signal having a predetermined relationship to the rate at which the rotor turns. In the patented structure the light radiating and receiving source is mounted in an annular ring that fits onto the glass cover of the meter.
U.S. Pat. No. 4,415,853 discloses a scanner device mounted so as to detect the presence of a marking on the rotating disc and therefrom generate a pulse signal. In this patented structure, as in the two previously mentioned patented structures, the light source and receiver are of considerable distance from the rotating disc by virtue of the fact they are external to the meter cover. They are furthermore located in the vicinity of the glass cover making them susceptible to extraneous radiation source signals. Also by virtue of the fact they are located in surrounding relation to the exposed part of the meter they are subjected directly to ambient conditions as well as being prone to vandalism or unwanted manipulation.
A further form of pulse initiator is disclosed in U.S. Pat. No. 3,943,498.
In all of the foregoing, the pulse initiator is either disposed internally of the meter along with other electronic components to enhance the meter's function or is located externally of the meter at a position forwardly of the base of the meter in proximity to the glass cover.
Since the traditional residential meters are very reliable and economical it is not cost effective to replace them with solid state meters at present. Hence, enhancing a meter's function involves counting the meter's disc revolutions and using a micro-processor to manipulate this information to produce the rate structures or features required. Adding these electronics to a meter reduces the meter life in the field. At present a plain electromechanical meter is expected to last 30 to 45 years while the life of an electronic meter is substantially less. Adding electronics also increases the amount of testing required by regulatory authorities to verify the calibration (seal) with each meter having to be done individually.
An object of this invention is to provide means external to a simple electro-mechanical meter for initiating a pulse in response to the disc revolutions but which is disposed in a secure location and in close proximity to the rotating disc.